early 15c., from Middle French compulsion, from Latin compulsionem (nominative compulsio) "a driving, urging," noun of action from past participle stem of compellere "compel" (see compel). Psychological sense is from 1909 in A.A. Brill's translation of Freud's "Selected Papers on Hysteria," where German Zwangsneurose is rendered as compulsion neurosis.

compulsion com·pul·sion (kəm-pŭl'shən)n. An uncontrollable impulse to perform an act, often repetitively, as an unconscious mechanism to avoid unacceptable ideas and desires which, by themselves, arouse anxiety.